The present invention relates to an improved transmission mechanism for adjusting the inclination angle of the leaves of venetian blinds.
Please refer to FIGS. 6 and 7. Conventional venetian blinds are controlled by two ropes (R) and four strings (S1) (S2). The ropes (R) are used to lift the whole venetian blind up, while the strings (S1) (S2) control the inclination angle of the leaves (L) to adjust the entry of the light. The two strings are tied to a string attacher (SA) which is fixed to a rotary beam (B) in a string-hanger (SH) in the top bar (T). When the user rotates an adjusting rod (A), the torque will be transmitted througha gearbox (GB) to the rotary beam (B), so that the latter will be rotated around its own axis. The rotation of the rotary beam (B) causes one of the strings (S1) to rise and the other one to descend, thus the inclination angle of the leaves will change.
In the conventional venetian blind, all the leaves are adjusted as an entity. In other words, all the leaves are adjusted simultaneously to the same inclination. However, in some cases, not all the leaves are desired to adjust to the same inclination. Sometimes it is preferred that the leaves of the upper half of the venetian blind be kept horizontal to allow light to enter while the leaves of its lower half are adjusted to a steep inclination to intercept the light so that some of the articles in the room which are vulnerable to radiation may not be exposed to the sunlight. For this purpose, the applicant developed an adjusting mechanism for adjusting the inclination of the leaves. It comprises two rotary beams (B1) (B2). The leaves of the upper half of the venetian blind are controlled by a first set of strings (S1') (S2') which are tied to the first rotary beam (B1), while the leaves of the lower half thereof are controlled by a second set of strings (S1") (S2") which are tied to the second rotary beam (B2). The gear box (GB) and string-hangers (SH) are provided with a plurality of gears to enable one of the rotary beams (B1) (B2) to mechanically connect with the adjusting rod (A) and the other one thereof to mechanically disengaged therewith. Thus the user can selectively adjust the leaves of the upper half or the lower half of the venetian blind. This device was applied for patent in the United States (Ser. No. 06/687,763 now abandoned).
Such a device enables the upper and lower part of a venetian blind to be adjusted separately. However, its structure is relatively complicated and necessitates a number of gears whic not only exist in the gear box (GB), but also exist in each string-hanger (SH). These elements are crowded in the narrow space of the string-hander so that the strings are liable to be jammed among the gears in the string-hanger.
Accordingly it is the object of the product invention to provide an improved gear box to selectively connect any one of the two rotary beams (B1) and (B2).
According to the present invention, each of the rotary beams (B1) (B2) is provided with a gear which is axially slidably but not rotatably mounted on the rotary beams. Both gears are retained in a shifting member and can be shifted axially by the latter between a first and a second position. The gear box is provided with an internal gear which is mechanically connected to the adjusting rod (A). When the shifting member is in its first position, the gear of the first rotary beams (B1) is engaged with the internal gear. Thus the upper half of the venetian blind can be adjusted by rotating the adjusting rod (A). When the shifting member is in its second position, the gear of the second rotary beam is engaged with the internal gear. Thus the lower half of the venetian blind can be adjusted by rotating the adjusting rod. The axial shift of the retaining member is achieved by a cord. Preferably, the internal gear is provided inside a cylindrical body which forms a crown gear at its one end. The shifting member can be received inside the cylindrical body so that the space is optimally utilized. A bevel gear engages with the crown gear. The bevel gear is connected to the adjusting rod and co-rotates with the latter. Preferably, the bevel gear and the adjusting rod are hollow to allow the cord to extend to the outside through the bevel gear and the adjusting rod.
This invention will be better understood when read in connection with the accompanying drawing, in which: